Fix version comparison in Version.pm

Version strings with unequal numbers of parts were being compared
incorrectly. We cure this by treating a missing part in the shorter
version as 0.

per complaint from Jehan-Guillaume de Rorthais, but the fix is mine, not
his.

Discussion: https://postgr.es/m/20220628225325.53d97b8d@karst

Backpatch to release 14 where this code was introduced.

Author: adunstan

src/test/perl/PostgreSQL/Version.pm

@@ -123,9 +123,12 @@ sub _version_cmp
 
 	for (my $idx = 0;; $idx++)
 	{
-		return 0 unless (defined $an->[$idx] && defined $bn->[$idx]);
-		return $an->[$idx] <=> $bn->[$idx]
-		  if ($an->[$idx] <=> $bn->[$idx]);
+		return 0
+		  if ($idx >= @$an && $idx >= @$bn);
+		# treat a missing number as 0
+		my ($anum, $bnum) = ($an->[$idx] || 0, $bn->[$idx] || 0);
+		return $anum <=> $bnum
+		  if ($anum <=> $bnum);
 	}
 }